The present invention relates to key-actuated locks in general, and more in particular, to key-actuated locks of the type that use a rotatable plug cylinder in a body and tumblers that interfere with rotation of the cylinder to effect a lock.
Key-actuated locks use a plug cylinder rotatable in a body and movable tumblers that interfere with rotation of the cylinder with respect to the body and, consequently, the actuation of some opening device, such as a latch or bolt. Bits of the key actuate the tumblers to permit unlocking. The bits displace the tumblers radially with respect to the axis of rotation of the cylinder. With the right key, the tumblers move out of the rotational path of the cylinder and permit rotation of the cylinder and the unlocking of the lock. Springs bias the tumblers into a locking position interfering with rotation of the cylinder. In greater detail, the tumblers have followers that engage the key bits and engage pins of the tumblers. When the boundaries of all of the pins and followers line up on the diameter of the cylinder, the cylinder can turn with respect to the body. The bits line the boundaries up. Lost motion and various other techniques may determine when, during rotation of the cylinder, the tumblers can prevent unlocking, but the general operation of the cylinder, tumblers, and body is as described.
Locks of this type are not immune from picking. In an effort to make picking more difficult, the displacement of the tumblers can be made to depend not only on the radial distance of the bits of a key from the axis of rotation of the cylinder plug, but also on the angle of the bit faces with respect to radial planes that pass at right angles through the axis of rotation; U.S. Pat. Nos. 3,499,302 and 3,499,303 illustrate this technique.
To make it harder to drill out locks and open them that way, locks have drill shields and gates within the lock that block access to portions of the lock sensitive to being drilled.